Once again that list pertains to International trade of weapons used by Defense and military purposes, both for export and import. You are making this a big deal all about nothing.
It's all spelled out in black and white.
The point is the game has changed by the issuance of the guidance letter. It is not now limited to export and import, but includes manufacturing without subsequent export or intent to export. The PDF of the letter is contained in the link in the first post of this thread. Below is the applicable excerpt.
"In response to questions from persons engaged in the business of gunsmithing, DDTC has found in specific cases that ITAR registration is required because the following activities meet the ordinary, contemporary, common meaning of “manufacturing” and, therefore, constitute “manufacturing” for ITAR purposes:
a) Use of any special tooling or equipment upgrading in order to improve the capability of assembled or repaired firearms;
b) Modifications to a firearm that change round capacity;
c) The production of firearm parts (including, but not limited to, barrels, stocks, cylinders, breech mechanisms, triggers, silencers, or suppressors);
d) The systemized production of ammunition, including the automated loading or reloading of ammunition;
e) The machining or cutting of firearms, e.g., threading of muzzles or muzzle brake installation requiring machining, that results in an enhanced capability;
f) Rechambering firearms through machining, cutting, or drilling;
g) Chambering, cutting, or threading barrel blanks and:
h) Blueprinting firearms by machining the barrel."
